A self-luminous organic EL display employing an organic light emitter such as diamines has been the focus of attention as a flat display in recent years. As shown in FIG. 1 for example, this organic EL display has a structure that an EL element substrate 1 made of glass has one of the surfaces (an inner surface) formed with, sequentially from the bottom layer side, a lower electrode 2 in a parallel striped pattern, an organic light-emitting layer 3, and an upper electrode 4 in a parallel striped pattern extending along an orthogonal direction to the lower electrode 2, and that between peripheral portions of the EL element substrate 1 and a sealing glass plate 5 arranged opposed thereto are sealed by a sealing layer 6.
This kind of organic EL display has many advantages; the display has high luminance, high contrast, and excellent display recognizability, can be formed extremely thin in thickness, is applicable also to an ultra-thin display having a total thickness of 1 mm or thinner for use in small devices such as a cell-phone (a cellular mobile telephone) and a digital camera, can be constructed of solid materials in its entirety, and is driven with direct current, so that a driving circuit thereof is simplified. On the other hand, there is a drawback that luminescence characteristics of the organic EL element are significantly deteriorated by contact with moisture. Therefore, the organic EL element needs to be strictly cut off from the outside air.
At present, a sealing method with use of a glass frit and a laser is considered to be the leading candidate as a sealing means for the organic EL display. That is, the glass frit is such that a powder mixture whose components are mainly metal oxides is heated, melted, vitrified, and then finely pulverized. This powder is brought into a paste form and coated on a sealed portion and melted again by heating to form a sealing glass layer. While a sealing temperature of a general glass frit is 400° C. or more, the organic EL display may have a problem in sealing by in-furnace heating that an organic EL element is damaged or thermally degraded under the influence of high temperature. Thus, a method is suitable that a laser beam is irradiated on panel peripheral portions between which the glass frit intervenes, and only sealed portions are locally heated to melt the glass frit.
In this laser sealing, a glass frit with high absorbability of a laser beam is preferably used in achieving good sealing quality. In terms of this, a vanadium-based glass frit having a color tone of dark brown or seal brown is seen as promising. A variety of glass compositions have been proposed as the vanadium-based glass frit heretofore. For example, Patent Document 1 discloses a glass frit which is of a V2O5—P2O5—Bi2O3 system and has an optional component of oxides of Zn, Te, alkali metal, and alkaline earth metal. Patent Document 2 discloses a glass frit which is of a V2O5—P2O5 system and has an optional component of oxides of Sb, Fe, K, Ti, Al, B, W and Bi. Patent Document 3 discloses a glass frit which is of a V2O5—TeO2—BaO—WO3 system and a V2O5—TeO2—BaO—ZnO—Sb2O3 system and has an optional component of oxides of P, Sr, Ge, La, Cr, Nb, Y, Mg, Ce, Er, etc. Patent Document 4 discloses a glass frit which is of a V2O5—TeO2—P2O5 system and has an optional component of ZnO and BaO. Patent Document 5 discloses a glass frit which is of a V2O5—TeO2—Ag2O system and has an optional component of oxides of P, Ba, Zn, K, W, Fe, Mn, Sb, etc. Further, the present applicant has previously proposed, as Patent Document 6, a lead-free glass material for organic-EL sealing, which is of a V2O5—ZnO—BaO—TeO2 system and has an optional component of oxides of Nb, Al, Si, Mg, Sb, Cu, and Sn and also contains Nb2O5+Al2O3 at a specific range.
The vanadium-based glass frits disclosed in Patent Documents 1 to 5 have a composition containing P2O5 as an essential component or a particularly preferable optional component, and accordingly have a drawback that water resistance of sealed glass portions having been melted again is insufficient and moisture enters inside with time to bring about a reduction in luminescence characteristics of the organic EL element. Further, a glass frit preferably has a lower softening temperature in order to reduce the thermal adverse effects on the organic EL element even in the case of the laser sealing, preferably has a thermal expansion coefficient closer to that of a glass substrate which is an object to be sealed, in order to ensure the sealing and enhance the sealing strength, and is preferably highly stable and less likely to undergo a crystal deposition during melting in order to loosen conditions in performing the sealing continuously and suppress occurrence of an error. Hence, the conventional glass frits cannot exhibit satisfactory performance in terms of low-temperature softening properties, thermal expansion coefficients, stability, etc.